Currently, if we don't configure the build with --with-vendor-version=XXX the 'java.vendor.version' property won't be set at all, which violates the spec. Setting it to an empty string will be ignored and has the same behavior like not setting it at all. This also makes default OpenJDK builds (which haven't been configured with --with-vendor-version non-compliant).

The fix is trivial: unconditionally set the 'java.vendor.version' property to the value of VENDOR_VERSION_STRING in VersionProps.java.template, even if VENDOR_VERSION_STRING is the empty string (which is the default if --with-vendor-version wasn't given at config time.